Over time the focus of the protests has moved from demands for the return of the students to spasms of disbelief in the government.
Photograph: Marco Ugarte/AP

Mexico is facing an escalating political crisis amid growing fury over a mansion built for the presidential family and the disappearance and probable massacre of 43 student teachers.

The two apparently unrelated issues have fed the widespread perception that unbridled political corruption is the underlying cause of the country’s many problems – ranging from stunted economic growth to a breakdown of law and order that has left parts of the country at the mercy of murderous drug cartels.

“The drama of Mexico is about impunity,” said leading political commentator Jesús Silva Herzog. “This is not about the popularity or unpopularity of the president, that is irrelevant. It is about credibility and trust and, at its root, it is about legitimacy.”

Thousands gathered in Mexico City on Thursday ahead of what was expected to be the largest demonstration so far over the students’ forced disappearance by municipal police in collusion with a local drug gang in the southern city of Iguala.

Classmates of the missing students have spent the past week traveling the country in an effort to start unifying the diverse protest movement around clear goals for future change. On Thursday night, three groups of students are due to lead separate marches which will converge at the capital’s main Zócalo plaza around nightfall.

“Beyond the lies of the government, we have the possibility to start moving an entire country towards change,” student Omar Garcia told MVS Radio in the morning.

Protests were also planned in other major Mexican cities and around the world.

Preparations for the march dominated social media in Mexico with Twitter users posting slogans such as “There will not be a mass grave big enough to shut us all up.”

A large, peaceful march in Mexico City on 8 November ended in violence with masked youths torching the wooden door of the ceremonial presidential palace. Many protestors claimed the assault was provoked and circulated photographs and videos showing alleged government agents who had participated in it but later slipped behind police lines.

Ahead of the main demonstration, an attempt to blockade Mexico City’s airport by a few hundred protestors was abandoned after a large contingent of riot police blocked their way.

While the focus of the protests is indignation over the government’s handling of the disappearance of the 43 students, there is also significant anger over its clumsy efforts to dismiss serious allegations of a conflict of interests involving President Enrique Peña Nieto himself.

“I don’t want this to continue to be a pretext for offending and defaming my family,” she said.

Rivera said she had been paying for the house from the fruits of her labour earned during a 25-year-long career within TV giant Televisa that ended in 2010 with the payment of 88.6 million pesos ($6.5m) and the transference of property of another luxurious residence that backs onto the controversial new mansion.

She said she had already paid about a third of the cost of the new home worth 54 million pesos ($4m), in accordance with a contract signed with the company over eight years.

She said she had met the company’s owner, who also happens to be a personal friend of the president, “like I meet many businessmen, professionals and artists”.

But the first lady’s attempt to turn the page of the scandal was met with widespread skepticism.

“There have always been rumours, but we have never before had documents that suggest that a president in office has participated in illegal operations,” commentator Silva Herzog said, adding that he expected the unanswered key question to further fuel public skepticism and anger.

“This is the worst possible moment for a scandal of this kind.”

On Wednesday night, President Peña Nieto showered praise on his wife’s “bravery” in revealing details of her personal accounts despite not being legally obliged to do so.

He then announced he would be doing the same because “I value the trust of Mexicans more than the right to confidentiality that I could obtain as a public servant,” he said. The assets, uploaded later on the presidential website, include four houses and an apartment.

The students went missing after being arrested by municipal police who also participated in a series of attacks during the night that left six people dead.

The disappearance of the students has sparked numerous demonstrations in many parts of the country. Over time the focus of the protests has moved from demands for the return of the students alive, to disbelief at the government’sfailure to crack down on widespread collusion between law enforcement agencies and drug mafias.

These latest demonstrations have been much more widespread than the protests prompted by allegations of fraud in Peña Nieto’s electoral victory in 2012.

Unlike during the previous wave of dissent, the current protests have expressed anger at perceptions of corruption across the entire political class that is viewed as corrupt, not just Peña Nieto.

The president had previously adopted a conciliatory tone, expressing sympathy for the victims’ families and promising a full and thorough investigation, but on Tuesday he used a speech to denounce violent outbreaks in some of the numerous demonstrations in recent weeks.

The violence, he said, “appears to respond to a general interest to destabilise and, above all, attack the national project that we are pushing forward”.

The harder line echoes some calls in the national press by commentators such as Ricardo Alemán, who has begun regularly urging politicians to discard their “fear of governing” and crack down radical elements in the demonstrations.

Other analysts, however, detect a menacing tone in the president’s words.

Silva Herzog drew parallels with the language used by President Gustavo Díaz Ordaz, who governed at the time of the watershed 1968 Tlatelolco massacre in which scores – and possibly hundreds – of pro-democracy students were killed by government forces in Mexico City.

“It is dangerous because it polarises the climate,” he said. “The solution has to start by recognising the legitimate foundations of the collective irritation. The country has good reason to be angry.”

With Thursday’s key demonstration approaching on the 104th anniversary of the Mexican revolution, the authorities announced the cancellation of the annual military parade that usually fills the capital’s central streets on that day.